This invention relates to hydraulic hammers of a type used to break up concrete, street pavement, building walls and the like. More particularly, it relates to a linear actuator for providing the impacting force on the moil of hydraulic hammers and similar impact devices. Even though this invention relates specifically to an actuator for impact devices, it might be useful to understand the construction and operation of an impact device per se, such as a hydraulic hammer, in order to more fully appreciate this invention. Therefore, the entire teaching of my U.S. Pat. No. 4,231,434, issued Nov. 4, 1980, is incorporated herein by reference, and many two digit numerals therein are also used to designate corresponding parts in this invention.
A problem with prior impact devices resides in the manner force is applied to the ram which strikes the moil. Specifically, an air spring or chamber of compressed gas forces a metal plate, which forms a reciprocating wall of a chamber, directly against the ram head to produce the desired energy of the ram against the moil and thence against the target material. This impact force of the ram against the moil often also produces a re-vibratory reaction force by the ram head back against the driven plate. Repeated operation of such equipment causes metal fatigue in the plate contacting the ram head resulting in unwanted down time, maintenance and a shortened working life of the plate and ram.